Tundish slag stopper assemblies, including a slag stopper chamber generally above and surrounding the tundish drain and a piston driven stopper plunger penetrating the stopper chamber directly above the drain, are used in some tundishes for reducing slag and for stopping and starting the flow of liquid metal through the tundish drain. By way of background, a conventional tundish vessel 10, shown in FIG. 1, includes a floor 20, a front wall 12, a back wall 14, two side walls 16 and 18, an impact region 22, and a drain 24. An impact pad 26 having a sinusoidal upper surface helps reduce splashing and turbulence caused by pouring molten metal into the impact region 22. An upright baffle 28 helps regulate the flow of molten metal leaving the impact region 22 and proceeding toward the drain 24.
Referring to FIG. 2, the inside of the conventional tundish vessel 10 is lined with a refractory liner 11 adjacent to the outer steel shell 13. The drain 24 includes a drain nozzle 23, a refractory drain block or block assembly 25 above and surrounding the drain nozzle 23, and a layer of refractory binder or cement 27 between the drain block 25 and the nozzle 23. Flow of molten metal through the drain nozzle 23 is regulated using a stopper plunger 30. The stopper plunger 30, also shown in FIG. 8, includes an elongated piston 32 which can be raised and lowered by conventional techniques known in the art, and a wider drain stopper 34 connected to the piston 32.
Above and surrounding the drain block 25, and surrounding the stopper plunger 30, is a stopper chamber 40 used for keeping impurities known as "slag" from mixing with the molten metal which exits the drain 24. The stopper chamber 40, shown in FIGS. 2 and 6, includes a lower rim 42 surrounding the drain block 25, a center opening 44 for receiving and slidably engaging the piston 32, and a slanted, preferably conical or frustro-conical wall 46 between the rim 42 and the center opening 44. A plurality of smaller openings 48 for receiving molten metal are located in the slanted wall 46, preferably closer to the lower rim 42 than to the center opening 44. Because slag tends to float toward the top of the tundish, the amount of slag passing through the drain is minimized by allowing molten metal to enter the chamber 40 only through openings 48 located very near to the floor 20 of the tundish vessel.
The amount of space between the piston 32 and the inner wall 45 of the central opening 44 is just enough to permit the piston 32 to comfortably slide back and forth through the opening 44. When the drain is closed, the piston 32 is in a fully extended position as shown in FIG. 2. When the drain is open, the piston 32 has conventionally been in a fully retracted position as shown in FIG. 3. In other words, when the drain is open, the piston 32 has typically been raised until the wider drain stopper 34 comes into contact with the narrow top region of the slanted wall 46 of the chamber 40, as shown in FIG. 3.
In the conventional apparatus described above, some contamination of the molten metal leaving the tundish drain has resulted from the presence and operation of the stopper plunger 30. First, the space between the plunger piston 32 and the inner wall 45 of the center opening, though small, nevertheless permits some slag and lower purity molten metal to pass through the center opening 44 and into the chamber 40 due to suction from the drain. Second, the movement of the piston 32 between the fully retracted position shown in FIG. 3 and the fully extended position shown in FIG. 2 helps drag some of the impurities through the center opening 44. Third, wear and tear on the piston 30 and chamber 40 is facilitated by extensive movement of the piston 30, causing refractory contaminants to chip or erode away from these mechanical components.